Gold Nanoparticles Supported on Polyacrylamide Containing a Phosphorus Ligand as an Efficient Heterogeneous Catalyst for Three-Component Synthesis of Propargylamines in Water

Article abstract of DOI:10.1055/s-0035-1561286

Gold nanoparticles supported on a polyacrylamide containing a phosphinite ligand have been synthesized and characterized using different techniques such as TEM, SEM, EDX, XPS, and solid UV analyses. The new material was successfully applied as a heterogen

Full text of DOI:10.1055/s-0035-1561286

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2016, 27, A–I
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Gold Nanoparticles Supported on Polyacrylamide Containing a
Phosphorus Ligand as an Efficient Heterogeneous Catalyst for
Three-Component Synthesis of Propargylamines in Water
Mohammad Gholinejad*a
Fatemeh Hameda
Carmen Nájera*b
a Department of Chemistry, Institute for Advanced Studies
in Basic Sciences (IASBS), P. O. Box 45195-1159, Gavazang,
Zanjan 45137-6731, Iran
gholinejad@iasbs.ac.ir
b Departamento de Química Orgánica and Centro de
Innovación en Química Avanzada (ORFEO-CINQA),
Universidad de Alicante, Apdo. 99, 03080 Alicante, Spain
cnajera@ua.es
Received: 23.09.2015
Accepted after revision: 18.11.2015
Published online: 28.12.2015
acetylides with the situ generated imines or iminium ions,
from the corresponding primary or secondary amines, is a
very useful method for the preparation of propargyl-
amines.13 Li and coworkers reported unique property of
gold in activation of alkynes in the three-component A3
coupling reaction of an aldehyde, an alkyne, and an amine
for the preparation of propargylamines.14 After reporting
this procedure, different homogenous gold catalysts have
been introduced in A3 coupling reactions.15 However, de-
spite the efficiency of some of these reports, homogenous
catalysts suffer from the problem of recovery and catalytic
reuse which is economically important for expensive metal
catalysts such as gold. Nevertheless, limited heterogeneous
gold catalysts have been reported in A3 coupling reactions.16
Nowadays, polymeric materials have been successfully
applied as promising support for the stabilization of metal
nanoparticles with a controlled size distribution.17 Along
this line, different polymeric structures have been used for
supporting gold nanoparticles.18 Particularly, phosphorus
compounds and therefore polymers containing phosphorus
atoms are excellent ligands for stabilization of gold cata-
lysts.19 Recently, we have reported the synthesis and appli-
cation of polymer containing phosphorous and nitrogen li-
gands as a support for stabilization of palladium nanoparti-
cles and its applications in Suzuki–Miyaura and
Sonogashira–Hagihara coupling reactions.20 Also, we have
recently reported that gold and copper catalysts supported
on periodic mesoporous organosilica with ionic liquid
framework (PMO) as an efficient and recyclable catalysts
for the three-component coupling reaction of aldehydes,
alkynes, and amines in chloroform.21 In continuation with
our interest on heterogeneous gold reactions and A3 cou-
pling reaction, herein, we wish to report the synthesis,
characterization, and application of a polymer containing
phosphorous and nitrogen ligands as an excellent support
DOI: 10.1055/s-0035-1561286; Art ID: st-2015-u0756-c
Abstract Gold nanoparticles supported on a polyacrylamide contain-
ing a phosphinite ligand have been synthesized and characterized using
different techniques such as TEM, SEM, EDX, XPS, and solid UV analy-
ses. The new material was successfully applied as a heterogeneous cata-
lyst for the three-component A3 coupling of amines, aldehydes, and
alkynes to give propargylamines. Reactions are performed in neat wa-
ter at 80 °C with only 0.05 mol% catalyst loading. The heterogeneous
catalyst is recyclable during seven consecutive runs with small decrease
in activity.
Key words gold nanoparticles, alkynes, propargylamines, multicom-
ponent reaction, polyacrylamide
Over the past few decades, transition metals have had
great impact on the development organic chemistry
through the introduction of new multifarious catalytic re-
actions.1 Gold is one of these transition metals which cata-
lytic properties have been developed recently as a source of
heterogeneous or homogeneous catalysts.2 Along this line,
oxidation of alcohols3 and carbon monoxide,4 hydrogena-
tion of olefins,5 cycloaddition reactions,6 carbon–heteroat-
om bond formation,7 cyclization of enynes,8 deoxygenation
of epoxides to alkenes,9 and different coupling reactions
such as Sonogashira10 and Suzuki11 reactions are some of
the notable applications of gold as a catalyst. Moreover,
gold catalysts are well known for their ability to promote
activation of C–H bonds for the formation of carbon–carbon
or carbon–heteroatom bonds.12
Because of extensive pharmaceutical relevance of prop-
argylamines and importance as building blocks in the
preparation of nitrogen-containing molecules as well as key
intermediates for natural product synthesis, in recent years,
great effort has been paid to the synthesis of these com-
pounds. The multicomponent A3 reaction of metal–
© Georg Thieme Verlag Stuttgart · New York — Synlett 2016, 27, A–I

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M. Gholinejad et al.
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for the stabilization of gold nanoparticles and its applica-
tion as a recyclable catalyst in A3 coupling reactions in neat
water.
Diffuse reflectance UV visible spectra (DR UV-Vis)
showed disappearance of related peaks to gold(III) at λ =
230 and 320 nm confirming reduction of gold(III) to gold(0)
particles (Figure 2).22
The polymer containing P,N ligands was synthesized by
reaction of 2-aminophenol with acryloyl chloride in the
presence of Et3N in dry THF producing N-(2-hydroxyphe-
nyl) acrylamide (1). The resulting acrylamide 1 was allowed
to react with chlorodiphenylphosphine (PPh2Cl) using t-
BuOK as a base in t-BuOH as solvent. The obtained phosphi-
nite 2 was subjected to polymerization using 2,2′-azobis-
isobutyronitrile (AIBN) as initiator in t-BuOH for 24 hours at
70 °C to afford the final polymer containing P,N ligands 3
(Scheme 1).20
OH
OH
H
O
NH2
+
N
Et3N, THF
PPh2Cl
Cl
t-BuOK,
t-BuOH,
r.t., 1 d
O
0–25 °C, 2 h
1
Figure 2 DR UV-vis spectra of the polymer-supported gold nanoparti-
cles
n
OPPh2
CO
SEM image of the material showed the formation of
large sheets in microscale dimension (Figure 3). Further-
more, energy dispersive spectroscopy (EDS) analysis of cat-
alyst obtained from SEM confirmed the presence of gold
species in the polymer-supported gold nanoparticles (Fig-
ure 4).
HN
H
N
Ph2PO
AIBN, t-BuOH
O
70 °C, 1 d
3
2
Scheme 1 Synthesis of polymer 3
The final polymer-supported gold nanoparticles were
easily obtained by treating 3 with NaAuCl4·2H2O salt in
aqueous media at room temperature. Thermogravimetric
analysis of the obtained material showed thermal stability
and negligible leaching of organic groups up to 250 °C (Fig-
ure 1).
Figure 1 Thermogravimetric diagram of the polymer-supported gold
nanoparticles
Figure 3 SEM image of the polymer-supported gold nanoparticles
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ence of phosphorous atoms in the polymer structure is re-
sponsible for reduction and formation of gold nanoparti-
cles.23
In the case of the X-ray photoelectron spectrum (XPS)
the material showed two doublet peaks for Au 4f7/2 and Au
4f5/2. The first doublet with peaks at 84.0 and 87.7 eV are
the characteristic peaks for metallic gold and the second
doublet at near 85.8 and 89.5 eV are due to Au3+ species.24
As seen in Figure 6 most of the gold is presented in the
gold(0) state.
Figure 4 EDS spectrum of the polymer-supported gold nanoparticles
The catalytic activity of polymer-supported gold
nanoparticles was assessed as a heterogeneous catalyst in
the A3 coupling reaction of amine, aldehyde, and alkyne. In
order to find optimized reaction conditions, the reaction of
benzaldehyde, piperidine, and phenylacetylene was select-
ed as a model reaction, and effects of solvents, catalyst
amount, and reaction temperature were studied (Table 1).
HRTEM images of polymer-supported gold nanoparti-
cles showed the presence of highly monodispersed
nanoparticles in an average size of 3–5 nm (Figure 5). It is
worth mentioning that formation gold nanoparticles was
achieved without using any reducing agents, and the pres-
Figure 5 TEM image of polymer-supported gold nanoparticles
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Table 1 Study of Reaction Conditionsa
O
H
N
catalyst
+
N
solvent
H
Figure 6 X-ray photoelectron spectroscopy (XPS) of the polymer-sup-
ported gold nanoparticles
Entry
Au (mol%) Solvent
Temp (°C) Time (h)
Yield (%)b
1
0.5
toluene
DMF
MeCN
toluene
DMF
THF
100
100
80
80
80
70
70
80
80
80
80
80
80
60
50
24
24
24
24
24
24
15
24
24
24
24
24
24
24
24
91
11
24
40
10
18
90
98
99
99
98
97
80
60
18
Using 0.5 mol% of catalyst and toluene as a solvent at 100 °C
afforded 91% isolated yield and decreasing the reaction
temperature to 80 °C gave a lower 40% yield (Table 1, en-
tries 1 and 4). Using other solvents such as DMF, MeCN, and
THF at different temperatures lower yields were obtained
(Table 1, entries 2, 3, 5 and 6). However, using CHCl3 and
H2O the corresponding propargylamine was isolated in 90%
and 98% yields at 70 °C and 80 °C, respectively (Table 1, en-
tries 7 and 8). Thus, H2O was selected as the best solvent,
and then the effects of catalyst amount and reaction tem-
perature were studied. Decreasing the catalyst loading from
0.5 to 0.05 mol% did not affect reaction yield (Table 1, en-
tries 8–12). However, the use of 0.025 mol% of catalyst
caused a decreasing of yield to 80% at 80 °C (Table 1, entry
13). Also, using 0.05 mol% under lower temperatures afford
low yield for the reactions (Table 1, entries 14 and 15). As
conclusion, we selected H2O as a solvent and 0.05 mol% cat-
alyst at 80 °C as optimized reaction conditions.
2
0.5
3
0.5
4
0.5
5
0.5
6
0.5
7
0.5
CHCl3
H2O
8
0.5
9
0.4
H2O
10
11
12
13
14
15
0.2
H2O
0.1
H2O
0.05
0.025
0.05
0.05
H2O
H2O
H2O
H2O
a Reaction conditions: benzaldehyde (1 mmol), piperidine (1.5 mmol), phe-
nylacetylene (1.5 mmol), catalyst (see column), and solvent (2 mL).
b Isolated yield after column chromatography.
By using the optimized reaction conditions, the synthe-
sis of propargylamines derived from structurally varied al-
dehydes, secondary amines, and phenylacetylene was per-
formed (Table 2). Results on Table 2 indicated that various
aromatic aldehydes bearing both electron-withdrawing and
electron-donating groups such as 4-Cl, 4-Br, 4-OMe, 4-i-Pr,
4-Me, 3-Me, and 3,5-Me2 reacted efficiently with piperi-
dine to afford the corresponding propargylamines in good
to excellent yields (Table 2, entries 1–8). Reactions of 2-
chlorobenzaldehyde and 2,4-dichlorobenzaldehyde, as rela-
tively sluggish substrates, proceeded well and produced the
corresponding propargylamines in high to excellent yields
(Table 2, entries 9 and 10). Reaction of 1-naphthalenecar-
baldehyde with both piperidine and morpholine took place
efficiently giving the corresponding products in high isolat-
ed yields (Table 2, entries 11 and 12). In the case of the re-
action of furfural as aldehyde with piperidine and morpho-
line the desired propargylamines were isolated in excellent
yields (Table 2, entries 13 and 14). Heptanal as a represen-
tative example of aliphatic aldehyde reacted with piperi-
dine and phenylacetylene to afford the desired product in
90% isolated yield (Table 2, entry 15). Also, reaction of benz-
aldehyde with morpholine and pyrrolidine proceed well,
and the corresponding propargylamines were obtained in
88% and 98% isolated yield, respectively (Table 2, entries 16
and 17).25
For the study about the recycling properties of this
polymer-supported gold catalyst the standard reaction of
benzaldehyde, piperidine, and phenylacetylene in H2O at
Figure 7 Recycling of the catalyst for the reaction of benzaldehyde,
piperidine, and phenylacetylene
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80 °C was considered. Results indicated that this catalyst is
recyclable during seven consecutive runs of one day pre-
serving catalytic activity (Figure 7).
This result confirmed small leaching of catalyst to the solu-
tion and heterogeneous character of the catalyst. Further-
more, mercury poisoning for the reaction of benzaldehyde,
piperidine, and phenylacetylene was studied. For this pur-
pose after one hour (15%) reaction, mercury(0) (300:1 Hg
to Au) was added to the reaction mixture under optimized
reaction conditions. Analysis of the reaction after 24 hours
showed 29% yield. According the suppression of the reac-
tion, we think again that the reaction may mostly proceed
under heterogeneous conditions.27
In order to confirm the heterogeneous nature of the cat-
alyst hot filtration test for the reaction of benzaldehyde,
piperidine, and phenylacetylene was performed. For this
purpose after five hours reaction (39% yield), the catalyst
was removed from the reaction by filtration and obtained
aqueous solution was allowed to react for additional 24
hours. Results showed that the yield of reaction obtained
from hot filtration was increased just to 48% after 24 hours.
Table 2 Reactions of Structurally Different Aldehydes with Amines and Phenylacetylenea
NR2
2
R1CHO
R1
Au catalyst (0.05 mol%)
+
H2O, 80 °C
R22NH
Entry
R1CHO
R22NH
Product
Yield (%)b
O
1
98
H
N
H
N
N
N
N
Cl
O
2
3
4
98
98
97
H
N
H
Cl
Br
O
H
N
H
Br
OMe
O
H
N
H
MeO
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Table 2 (continued)
Entry
R1CHO
R22NH
Product
Yield (%)b
O
H
5
76
96
87
74
80
95
N
H
N
N
N
N
O
H
6
N
H
O
H
7
N
H
O
H
8
N
H
Cl
N
O
9
H
N
H
Cl
Cl
N
Cl
O
H
10
N
H
Cl
Cl
H
O
11
73
N
H
N
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Table 2 (continued)
Entry
R1CHO
R22NH
Product
Yield (%)b
H
O
O
12
89
N
H
N
O
O
O
O
13
14
15
94
91
90
N
H
H
N
O
O
O
O
H
N
H
N
O
O
O
H
N
H
N
O
O
O
16
88
H
N
H
N
O
O
17
98
H
N
H
N
a Reaction conditions: aldehyde (1 mmol), amine (1.5 mmol), phenylacetylene (1.5 mmol), catalyst (0.05 mol%), and H2O (2 mL) were heated at 80 °C during 1
d.
b Isolated yield after column chromatography.
© Georg Thieme Verlag Stuttgart · New York — Synlett 2016, 27, A–I

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In conclusion a new polymer-supported gold nanoparti-
cles catalyst has been synthesized, characterized, and used
as an efficient catalyst for three-component coupling reac-
tion of amines, aldehydes, and phenylacetylene. Reactions
proceed in water as a green solvent and high to excellent
yields were obtained. The catalyst was recycled during sev-
en consecutive runs, and hot filtration experiments indicat-
ed the heterogeneous nature of this polymeric catalyst.
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Acknowledgment
The authors are grateful to Institute for Advanced Studies in Basic Sci-
ences (IASBS) Research Council and Iran National Science Foundation
(INSF-Grant number of 94010666) for support of this work. C. Nájera
is also thankful to The Spanish Ministerio de Economia y Competitivi-
dad (MINECO) (projects CTQ2013-43446-P and CTQ2014-51912-
REDC), FEDER, the Generalitat Valenciana (PROMETEOII/2014/017),
and the University of Alicante for financial support.
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Supporting Information
Supporting information for this article is available online at
http://dx.doi.org/10.1055/s-0035-1561286.
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r.t. and then extracted with EtOAc (3 × 10 mL). The organic
phase was dried over anhydrous Na2SO4 and the solvent evapo-
rated. The resulting propargylamine was purified by column
chromatography on silica gel using EtOAc and hexane giving
270 mg (98% yield) of the pure product 1-(1,3-diphenylprop-2-
yn-1-yl)piperidine.26 1H NMR (400 MHz, CDCl3): δ = 7.57–7.71
(m, 2 H), 7.55–7.56 (m, 2 H), 7.30–7.43 (m, 6 H), 4.90 (s, 1 H),
2.65 (br s, 4 H), 1.64–1.67 (m, 4 H), 1.48–1.51 (m, 2 H). 13C NMR
(100 MHz, CDCl3): δ = 138.2, 131.8, 128.7, 128.3, 128.2, 128.1,
127.7, 123.2, 88.2, 85.7, 62.4, 50.7, 25.9, 24.3.
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(25) A mixture of benzaldehyde (0.100 mL, 1 mmol), piperidine
(0.160 mL, 1.5 mmol), phenylacetylene (0.165 mL, 1.5 mmol),
catalyst (5 mg containing 0.05 mol% Au), and H2O (2 mL) was
© Georg Thieme Verlag Stuttgart · New York — Synlett 2016, 27, A–I